1. Field of Invention
The invention relates to an ink jet head that records characters and figures using ink ejecting from nozzles and a method for producing the ink jet head.
2. Description of Related Art
Generally, an ink jet head has a plurality of ejection channels connected to nozzles. Ink is supplied to the channels. When a piezoelectric material defining the channels are deformed or ink is heated locally for vaporization, pressure is applied to ink in the channels, which causes ink to jet out from the nozzles.
For such an ink jet head, the piezoelectric material such as lead zirconium titanate, PZT is used for an actuator board having a plurality of channels disposed in parallel. The voltage is selectively applied to an electrode provided on a side wall of each channel, causing deformation of the side wall. (Refer to Japanese laid-open Patent Publication No.7-304178.)
To produce the above ink jet head, the actuator board made of the piezoelectric material is formed with a plurality of channels all cut in parallel to an equal depth. A conductive layer is formed on the entire surfaces of the actuator board including the inside of the channels by electroless plating. The conductive layer is divided according to the channels by grinding or laser processing, to form a plurality of electrodes and connecting terminals. The electrodes of the conductive layer are formed on the side walls of each channel, whereas the connecting terminals for connecting an electrode to a pattern cable on a board, such as a flexible printed circuit board, are formed on a surface opposite to the surface where the channels are formed. One of the connecting terminals is connected to a driving control part of the ink jet head recording device. In this arrangement, the driving control part outputs a voltage based on record data. The voltage is applied to the electrodes in each channel via pattern cable and contacting terminals, which deforms the side walls and causes the ink in each channel to jet out from the nozzles.
In this kind of ink jet head, a nickel layer, as the conductive layer (electrodes), is formed on all surfaces of the actuator board made of the piezoelectric material by electroless plating, and gold is plated on the nickel layer so as to aid soldering a pattern cable. Nickel has some degree of anti-corrosion against ink, but it is not enough. Gold on nickel facilitates to ionize nickel and serves as a protective layer to prevent the nickel layer from corroding.
However, in this manner, manufacturing steps are increased, and manufacturing costs are raised.
The invention provides an ink jet head having an improved corrosion resistance to ink and less workload, such as heat generation, at the driving control part, and a method of producing such ink jet head, while reducing manufacturing costs. The invention also provides an inexpensive ink jet head that can work at a lower voltage.
Specifically, the invention provides an ink jet head that may include an actuator board formed with a plurality of ejection channels for jetting ink droplets out therefrom, and a plurality of electrodes provided on the actuator board so as to give jet energy to ink in channels. Each of the electrodes may include a first layer made of a noble metal having a property of being formable directly on the actuator board and a second layer that includes the noble metal with a lower electrical resistance, the second layer being formed on the first layer.
The material used for the first layer has a property of being able to adhere directly to a piezoelectric element of the actuator board, such as PZT, but its resistance is comparatively large. On the other hand, the electrical resistance of the material used for the second layer is smaller than that for the first layer. Further, the material of the second layer is difficult to be formed on the piezoelectric element directly, but is easy to be formed on a noble metal containing phosphorus or boron. The invention enables the formation of a two-layer electrode by ingeniously making use of the properties of these two materials. This two-layer structure improves corrosion resistance to ink, and eliminates the necessity to form a conventional protective layer. Therefore, the number of manufacturing processes and costs can be reduced.
In addition, pattern cables are connected to the second layer of low resistance, enabling reduction of the workload at the driving control part. If the layers of the electrode are made of different metals, it may cause a difference in electric potential between the two layers, which are easily susceptible to corrosion. However, the invention uses the same metal for the two layers, and such problem can be resolved.
In a preferred aspect of the invention, the first layer is made of palladium and may include at least one selected from the group consisting of phosphorus and boron, and the second layer is made of pure palladium with a high purity of approximately 99.5% or more. In this arrangement, palladium containing phosphorus has a property of being able to adhere to the actuator board made of PZT. Therefore, it is used for the first layer that can be formed directly on the actuator board. Palladium not containing phosphorus is difficult to be formed directly on the actuator board, but is easy to adhere to the first layer that is made of palladium containing phosphorus. Better still, palladium has high corrosion resistance to ink and is of lower resistance, therefore, it is advantageous as a terminal electrode for connecting the driving control part.
In another preferred aspect of the invention, the actuator board forms a catalyst metal particle layer thereon, and the first layer is formed on the catalyst metal particle layer. The catalyst layer is, for example, comprised of a tin ion particle layer and a palladium particle layer by precipitation. This precipitation of the catalyst layer facilitates forming the first layer made of palladium containing phosphorus as a plating layer by precipitation.
In a further preferred aspect of the invention, the first layer is formed by electroless plating or physical vapor deposition, and the second layer is formed by electroless plating, electroplating, or physical vapor deposition. The first layer can be easily formed on the actuator board because electroless plating or physical vapor deposition is performed in or using a liquid of palladium containing phosphorus. The second layer can be also easily formed on the first layer because electroless plating, electroplating or physical vapor deposition is performed in or using a liquid of palladium containing no phosphorus. Since the actuator is coated with PZT, the second layer can not be precipitated without the formation of the first layer because lead included in PZT is a catalytic poison. On the other hand, when the first layer is formed on the actuator board, lead of PZT is covered and the second layer is precipitated.
In another preferred aspect of the invention, the ejection channels of the actuator board are defined with walls of a piezoelectric material electrically polarized in at least one part, the electrodes are formed on sides of the walls, and the ink jet head may further include: a connecting terminal to connect each electrode formed on a surface of the actuator board opposite to the surface of the ejection channels to a signal source. In this arrangement, the conductive layer can be formed continuously from the ejection side to the opposite side of the actuator board, and consequently it is readily formable.
In a further preferred aspect of the invention, a process of producing an ink jet head, the process may include the steps of forming a plurality of channels in an actuator board, and forming a conductive layer on the actuator board, dividing the conductive layer into a plurality of electrodes that correspond to each channel. The step of forming the conductive layer may include the steps of forming a first layer made of a noble metal having a property of being formable directly on the actuator board, and forming a second layer that includes the noble metal with a lower resistance on the first layer. In this process, the conductive layer of the first layer is formed on the entire surface of the actuator board having channels including the ejection channels. The conductive layer of the second layer is formed on the first layer similarly. Then, these conductive layers are divided to easily turn to the electrodes corresponding to the ejection channels on the actuator board. The electrodes are formed by radiation of a laser or a plasma process.
The invention provides an ink jet head that may include an actuator board having a plurality of channels defined by side walls made of a piezoelectric material electrically polarized in at least one part, the channels each having an open face disposed in a longitudinal direction; an electrode formed on a surface of the side walls parallel to a polarized direction, the electrode generating an electric field orthogonal to the polarized direction so as to deform the side walls in a direction of the channel width, and a cover plate that covers the open faces of the channels, the cover plate being fixed to the side walls. The cover plate may be made of one selected from the group consisting of forsterite and beryllia. In this arrangement, when the voltage is applied to the electrode on the side walls, an electric field, whose electric force is orthogonal to the polarized directions, is generated, the side walls are deformed in the direction of the width of the channel to increase volume in the ejection channel surrounded by the side walls, and ink droplets are jetted out. When the side walls are deformed in the direction of the width of the channel, a reaction to the cover plate is triggered. However, the cover plate may be made of forsterite (2MgOxc2x7SiO2) or beryllia (BeO) whose Young""s modulus is higher than that of the piezoelectric material used for the side walls. These materials prevent the side walls from deforming due to the reaction, allowing an expected ink jet pressure to be obtained. The expected ink jet pressure can be obtained at a lower voltage compared to the conventional one, and the structure related to the electrical mechanism can be generated inexpensively.
Comparing to PZT or PT, forsterite and beryllia have high Young""s modulus and are inexpensive. Therefore, the ink jet head can be provided inexpensively. In addition, forsterite contributes to weight saving of the ink jet head because it is light.